Water-stable Zn-based metal-organic framework with hydrophilic-hydrophobic surface for selective adsorption and sensitive detection of oxo-anions and pesticides in aqueous medium

Given the importance of surface-functionalized materials with improved adsorption and detection properties for targeted applications, we report herein the design and development of a water-stable luminescent Zn-based metal-organic framework (Zn-MOF) with the hydrophobic-hydrophilic surface property. The developed luminescent Zn(II)-MOF {[Zn(PA2-)(dmbpy)](DMF)}n was synthesized via a solvothermal method using pamoic acid (PA) and 5,5′-dimethyl-2,2′-bipyridine (dmbpy) with free functional groups (hydroxyl and methyl groups). Careful single-crystal structure analysis revealed a 3-dimensional hydrogen-bonded network with a one-dimensional channel and functionalized surface. The surface functionalization was achieved through rational choice of ligands bearing methyl and hydroxyl groups as suitable hydrophobic and hydrophilic functionalities respectively, leading to a stable MOF in the aqueous medium. The MOF was used as an adsorbent for selective adsorption of monovalent permanganate anion (MnO4-) over other polyvalent oxo-anions as well as an optical platform for the detection of oxo-anions (permanganate (MnO4-), dichromate (Cr2O72-) and chromate (CrO42-)) and pesticide (2,6-dichloro-4-nitroaniline (2,6-DCNA)) in the aqueous medium. Overall, a combination of luminescent nature and hydrophilic-hydrophobic surface property makes the developed Zn-MOF an interesting platform for environmental application.